ORDER BY ROW_NUMBER - sql

Question

UPD: thanks for all, topic closed, after sleeping I understand everything =)
I have a problem with understanding OVER clause and and ROW_NUMBER function. Simple table - name and mark. I want to calculate average mark for each name.
SELECT top 1 with ties name, ROW_NUMBER() over (PARTITION BY name ORDER BY name) as number
FROM table
ORDER BY AVG(mark) OVER(PARTITION BY name)
it will display something like this, and I understand why - that is what ROW_NUMBER() does
name|number
Pete 1
Pete 2
But if I write
SELECT top 1 with ties name, ROW_NUMBER() over (PARTITION BY name ORDER BY name) as number
FROM table
ORDER BY AVG(mark) OVER(PARTITION BY name), number
it will display
name|number
Pete 1
And this time I don't understand how ORDER BY works with ROW_NUMBER() function. Can somebody explain it to me?

Answer 1

You can certainly order by ROW_NUMBER column because the SELECT clause is evaluated before the ORDER BY clause. You can ORDER BY any column or column alias. This is why no error message was thrown (because it is valid).
SELECT name, ROW_NUMBER() over (PARTITION BY name ORDER BY name) as number
FROM #table
ORDER BY number
Evaluates to
name number
---------- --------------------
John 1
pete 1
pete 2
John 2
pete 3
OP's second example of row_number is not correct.
SELECT AVG(mark) OVER(PARTITION BY name), name, ROW_NUMBER() over (PARTITION BY name ORDER BY name) as number
FROM #table
ORDER BY AVG(mark) OVER(PARTITION BY name), number
Returns as expected because AVG is the first sort column followed by number.
name number
----------- ---------- --------------------
11 pete 1
11 pete 2
11 pete 3
17 John 1
17 John 2
Change the query to number DESC and pete is still first however the row numbers are descending order.
name number
----------- ---------- --------------------
11 pete 3
11 pete 2
11 pete 1
17 John 2
17 John 1
SQL Order of operations
FROM clause
WHERE clause
GROUP BY clause
HAVING clause
SELECT clause
ORDER BY clause

Answer 2

You can't ORDER BY the ROW_NUMBER directly: I don't know why you didn't get an error on this case, but normally you would. Hence the use of derived tables or CTEs
SELECT
name, number
FROM
(
SELECT
name,
ROW_NUMBER() OVER (PARTITION BY name ORDER BY name) as number,
AVG(mark) OVER (PARTITION BY name) AS nameavg
FROM table
) foo
ORDER BY
nameavg, number
However, PARTITION BY name ORDER BY name is meaningless. Each partition has random order because the sort is the partition
I suspect you want something like this where ROW_NUMBER is based on AVG
SELECT
name, number
FROM
(
SELECT
name,
ROW_NUMBER() OVER (PARTITION BY name ORDER BY nameavg) AS number
FROM
(
SELECT
name,
AVG(mark) OVER (PARTITION BY name) AS nameavg
FROM table
) foo
) bar
ORDER BY
number
Or more traditionally (but name is collapsed for the average)
SELECT
name, number
FROM
(
SELECT
name,
ROW_NUMBER() OVER (PARTITION BY name ORDER BY nameavg) AS number
FROM
(
SELECT
name,
AVG(mark) AS nameavg
FROM
table
GROUP BY
name
) foo
) bar
ORDER BY
number
You can maybe collapse the derived foo and bar into one with
ROW_NUMBER() OVER (PARTITION BY name ORDER BY AVG(mark))
But none of this makes sense: I understand that your question is abstract about how it works bit it is unclear question. It would make more sense if you described what you want in plain English and with sample input and output